1. Field of the Invention
The present invention relates to a device for improving the purifying liquid evaporation in an axially symmetric dosing module for an SCR device.
2. Description of the Related Art
Aftertreatment systems are, commonly, used to reduce emissions. The NOx reduction is mainly realized by a selective catalytic reduction (SCR) system. The required Ammonia (NH3) for the reduction of the NOx is usual injected as a liquid with dissolved UREA, commonly AdBlue or DEF (water with 32.5% UREA).
An example of axially symmetric evaporation device is given in EP2339137.
The evaporation of the liquid (water) and the decomposition (thermolysis and hydrolysis) of the UREA requires some energy. This energy is usually delivered by the exchange with hot exhaust gas. However, at lower exhaust gas temperature there is not only less available energy, although still sufficient, but the available temperature difference, between the exhaust gasses and the injected liquid, which enable the heat exchange is much reduced.
Another factor worsens the evaporation process, namely the fact that the heat transfer is less efficient at low mean gas velocities.
The overall result is a reduced of evaporation and associated effects of liquid wall films and risk of solid deposits. This is an unacceptable behavior due to wrong NH3 dosing to the SCR system and/or increased back pressure.